Whereas various methods and devices such as magnetic agitators, vortex mixers and the like are used for the mixing of macroscopic quantities of liquids, these are usually unsuited for microscopic quantities of liquids. In particular, such mixing principles cannot be integrated into existing sample processing systems.
In microfluidics, therefore, passive mixing methods and devices are mainly used. Such mixing methods and mixers used in chemical process technology, and also usually with continuous operating mode, are known for example from EP 1311341 B1 or EP 1390131 B1. These methods and mixers are usually unsuited for the mixing of small volumes of liquid.
A new method is described in US 2003/0175947 A1 and in the article “Bubble-induced acoustic micromixing” by Robin H. Liu et al., LAB Chip, 2002, 2, 151-157. This presents a device for the mixing of very small volumes of liquid (22 μl), having a chamber, filled with the liquids being mixed, and cavities peripherally arranged and connected to the chamber. In the area of the cavities, air bubbles are captured and placed in resonant oscillation by acoustic excitation, so that the surrounding liquid is also placed in motion, leading to a faster blending as compared to diffusion mixing. In the corresponding model, the authors presume that the microflow created in this way is based on the frictional forces at the boundary surface between the liquid and the gas bubble.
This same mixing principle is also the basis for publications WO 2006/105616 A1 and WO 2004/030800 A2.